JPS5941349B2 - Carrier color signal noise removal circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise removal circuit capable of removing noise from a carrier color signal in a color video signal.

Conventionally, there are noise removal circuits as described below for removing noise from a video signal including noise obtained from a magnetic recording/reproducing device or the like. That is, the noise removal circuit supplies the video signal to a low-pass P waver and a high-pass waver, respectively, and outputs the output of the high-pass waver when the absolute value of the input level is below a predetermined value. When the level is zero or above a predetermined value, it is supplied to a coring circuit (a type of nonlinear circuit) in which the relationship between the input level and the output level is linear, and the output of the low-pass demultiplexer and the output of the coring circuit are By supplying the signals to a synthesizer and adding them, a video signal from which noise, particularly high-frequency noise, has been removed is obtained. However,
In addition to insufficient separation of the signal component and noise component in the video signal with this conventional noise removal circuit, the signal component of the output of the high-pass wave filter is subject to large distortion in the coring circuit, so Fine brightness changes in areas where brightness changes are small, such as the background of the image, disappear, and as a result, a scaly pattern is created in the image corresponding to areas where brightness changes are gradual.

Moreover, on the contrary, smear occurs in an image corresponding to a portion where the brightness change is steep, and the sharpness of the image deteriorates. In order to remove noise from a video signal without suffering much image degradation, the signal component and noise component should be better separated, and then signal processing for noise removal should be performed. In this case, even if the signal is distorted, the resulting deterioration in image quality should be made so that it is not so noticeable from the human visual characteristics.

As a noise removal circuit that satisfies these conditions, the applicant has proposed a noise removal circuit using an orthogonal transform circuit as shown below.

That is, the noise removal circuit consists of a cascade circuit consisting of a series/parallel conversion circuit, an orthogonal conversion circuit, a nonlinear circuit (for example, a coring circuit), an inverse conversion circuit, and a parallel/serial conversion circuit. A video signal containing noise is supplied, and a video signal from which the noise has been removed is obtained from the parallel/serial conversion circuit. Here, orthogonal and inverse transformations will be explained.

Now, → If the block of the video signal sequence that is the input signal is represented by X, similarly the block of the output signal sequence is represented by Y, the orthogonal transformation matrix is represented by A, and the inverse transformation matrix is similarly represented by B. Therefore, if the input signal is orthogonally transformed, , Therefore, the inverse transform output is: Therefore, the transform coefficient, that is, the orthogonal transform output Y is a linear combination of the row vector and the input signal.

By the way, orthogonal transformations such as Warschu, Hadamard, etc. can be used as this orthogonal transformation, but the properties of the video signal can be extracted well and the inverse transformation can be performed in the same procedure as the transformation. The Hadamard transform having the following characteristics is suitable.

By the way, there is no problem if the video signal is a black and white video signal, but if it is a color video signal such as the NTSC system, the noise can be removed by feeding it as is to a noise removal circuit including the above-mentioned orthogonal conversion circuit. However, since the color video signal includes a carrier color signal with a different band in addition to the luminance signal, there are restrictions on the conversion order and the sampling frequency when processing the video signal by quantizing it, which makes the system difficult. Lack of flexibility. Therefore, the inventor of the present invention devised a noise removal circuit that separates a color video signal into a luminance signal and a carrier color signal, and removes noise from each signal separately using a separate orthogonal transform type noise removal circuit.

Such a noise removal circuit has the advantage of eliminating constraints on the conversion order or the sampling frequency when quantizing and processing a video signal. By the way, in the noise removal circuit for the carrier color signal of such a noise removal circuit, if the unit delay amount of the serial/parallel conversion circuit is made equal to the sampling period of the carrier color signal, the levels of the parallel outputs will be uneven. As the orthogonal transform circuit, a complex one with a high order configuration must be used.

In view of this, the present invention relates to a carrier color signal noise removal circuit that is suitable for application to a color video signal noise removal circuit, and attempts to propose a circuit that can simplify the configuration of the orthogonal transform circuit used. It is something to do. An embodiment in which the present invention is applied to a noise removal circuit for color video signals will be described below in detail with reference to the drawings.

FIG. 1 shows the overall configuration of the noise removal circuit. Reference numeral 1 denotes an input terminal to which a color video signal (NTSC color television signal) containing noise is supplied.

The color video signal from this input terminal 1 is sent to the A-D converter 2.
It is supplied to and sampled. The color video signal from the input terminal 1 is supplied to a synchronization separation circuit 3, from which a horizontal synchronization signal and a color burst signal are separated, and these signals are supplied to a clock signal generator. The clock signal from the clock signal generator 4 is supplied as a sampling signal to the AD converter 2 and the DA converter 14, which will be described later. The frequency of this clock signal is the color subcarrier frequency F8
O (-3.58MHz) or more, for example, 4 in this example.
Selected twice. The quantized color video signal output from the A-D converter 2 is supplied to a separation circuit 5, where it is separated into a quantized luminance signal and a quantized carrier chrominance signal, which are then sent to a luminance signal noise removal circuit 6A, respectively. and is supplied to the carrier color signal noise removal circuit 6B.

The luminance signal noise removal circuit 6A includes a first serial/parallel conversion circuit 7A, a first orthogonal conversion circuit 8A, and a first nonlinear circuit 9.
It is composed of a cascade circuit of A, a first inverse conversion circuit 10A, and a first parallel/serial conversion circuit 11A. The carrier color signal noise removal circuit 6B includes a second serial/parallel conversion circuit 7B, a second orthogonal conversion circuit 8B, a second nonlinear circuit 9B, a second inverse conversion circuit 10B, and a second parallel/serial conversion circuit. It is composed of 11B cascaded circuits. The luminance signal from which noise has been removed from the luminance signal noise elimination circuit 6A is supplied to the synthesizer 13 through the delay circuit 12, and is also supplied to the carrier chrominance signal noise elimination circuit 6.
The noise-removed carrier color signal from B is sent to this combiner 13.
, etc. are added, and the summed output is supplied to the output terminal 16 through the low-pass filter 15, thereby obtaining a color video signal from which noise has been removed.

Next, the circuits of each part of the noise removal circuit shown in FIG. 1 will be explained with reference to FIG. 2 and subsequent figures.

First, referring to FIG. 2, the separation circuit 5 will be explained. Although the separation circuit 5 can be configured with a low-pass P-wave device and a band-pass ▲-wave device that pass the luminance signal and the carrier color signal, respectively, in this embodiment, a separation circuit using a comb-shaped ▲-wave device is used. It is a circuit. The sampled color video signal from the above-mentioned A-D converter 2 is transmitted from the human input terminal 17 to the comb-shaped waveform transducer 18a.
, 18b, and their respective outputs are supplied to combiners 23 and 24. In the synthesizer 23, the output of the comb-shaped waveform generator 18a and the output of the other comb-shaped waveform waveform generator 18b are combined into a band-removal f-waveform unit 2 whose band center frequency is the color subcarrier frequency F8O.
2 is added to the output obtained from output terminal 2.
A luminance signal sampled at 5 is obtained. In the synthesizer 24, the output of the comb f-wave generator 18b is filtered by a band-removal wave generator 22.
is subtracted to obtain the sampled carrier color signal at output terminal 26. The comb-shaped waveform device 18a is the input terminal 17
The synthesizer 20 is configured to add the input signals of the above and the signals that are supplied to the delay circuit 19 and delayed by one horizontal period. Also, the other comb-shaped wave wave device 1
8b is configured such that the output signal from the delay circuit 19 is subtracted from the input signal from the input terminal 17 by the synthesizer 21. The band-eliminating f-wave filter 22 has a digital circuit configuration, and a specific configuration thereof is shown in FIG.

That is, each input signal from the input terminal 28 (for example, a 9-bit binary encoded signal) has a delay amount of 2 sampling periods.
It is supplied to the synthesizer 31 through the delay circuits 29-30 which are double the delay circuits, where it is added to the input signal from the input terminal 28, and the added output is supplied to the attenuator 32 with the attenuation ratio of +, and the synthesizer 33 Attenuator 32 from the output of delay circuit 29
so that the output of is obtained at the output terminal by directing it,
This band-eliminating wave filter 22 is configured. Next, the specific configuration of the serial/parallel conversion circuits 7A and 7B will be explained with reference to FIG.

The circuits 7A and 7B in FIG. 4 are used to convert a plurality of consecutive luminance signals and carrier color signals in a certain horizontal scanning section, for example, four This is a serial/parallel conversion circuit for orthogonally converting signals corresponding to unit areas (one unit area is, for example, one pixel). For the input signal Si from the input terminal 36, the delay amount is equal to the sampling period in the serial/parallel conversion circuit 7A for the luminance signal, and the delay amount is equal to the sampling period in the serial/parallel conversion circuit 7B for the carrier color signal. An output signal Si4 is obtained at an output terminal 40 through delay circuits 37-38-39 whose amount is equal to four times the sampling period, that is, equal to the color subcarrier period, and an output signal Si3 is obtained from the delay circuit 38 at an output terminal 41. The output signal Si2 is obtained from the delay circuit 37 at the output terminal 42, and the output signal Sil is obtained from the input terminal 36 at the output terminal 43, thereby forming the serial/parallel conversion circuits 7A and 7B. As mentioned above, since the unit delay amount of the serial/parallel conversion circuit 7B with respect to the carrier color signal is equal to the color subcarrier period, the parallel signals Si4 to Sil obtained at the output terminals 40 to 43 are as follows.
Since it corresponds to a signal for each color subcarrier period of the input signal (sampled carrier color signal) Si of the input terminal 36, each level thereof is the same.

Next, the serial/parallel conversion circuit 7A of the noise removal circuit in Fig. 1,
The parallel-to-serial conversion circuits 11A and 11B will be described with reference to FIG. 5 when the circuit 7B described in connection with FIG. 4 above is used.

49, 51, and 53 are parallel-to-serial converter circuits 11A for luminance signals whose delay amounts are equal to the sampling period, and parallel-to-serial converter circuits 1 for carrier color signals.
For 1B, the delay amount is 4 times the sampling period.
The delay circuit is equal to twice the color subcarrier period.

In the parallel/serial conversion circuits 11A and 11B, the input signal S''i1 from the input terminal 45 is transferred to the delay circuit 4.
9 and delay it, and its delayed output and input terminal 46
The synthesizer 50 adds the input signal S'I2 from the input terminal 47 and supplies it to the delay circuit 51, and the synthesizer 52 adds the delayed output and the input signal S'I3 from the input terminal 47 to the delay circuit 51. 53, and the delayed output and the input signal from the input terminal 48 are added in a synthesizer 54 to obtain an output signal S'1 at an output terminal 55. Next, another specific configuration of the serial/parallel conversion circuits 7A and 7B will be explained with reference to FIG.

The circuits 7A and 7B in FIG. 6 are used to convert luminance signals and carrier colors in a plurality of adjacent horizontal scanning sections, in this example two horizontal scanning sections, in the orthogonal transformation circuits 8A and 8B of the O-band noise removal circuit in FIG. 1. Serial/parallel conversion when performing orthogonal transformation of signals corresponding to a plurality of corresponding and continuous unit areas in a signal, for example two unit areas (one unit area is one pixel, for example), for example four unit areas in total. It is a circuit. A serial/parallel conversion circuit 7 converts the input signal Si from the input terminal 36 into a luminance signal.
In the case of A, the delay amount is equal to one horizontal period and the sampling period, and in the case of the serial/parallel conversion circuit 7B for the carrier color signal, the delay amount is one horizontal period and the sum of twice the sampling period and the sampling period. is delayed through delay circuits 57-58 equal to four times the output terminal 40.
output signal Si4 is obtained from the delay circuit 57 at the output terminal 41.
The output signal Si3 is obtained from the input terminal 36, and the delay amount is equal to the sampling period in the case of the serial-to-parallel conversion circuit 7A for the luminance signal and for the serial-to-parallel conversion circuit 7B for the carrier color signal. The output signal Si2 is supplied to the delay circuit 59 whose delay amount is equal to four times the sampling period, and output signal Si2 is obtained at the output terminal 42, and the output signal Sil is obtained from the input terminal 36 to the output terminal 43. It constitutes conversion circuits 7A and 7B. Next, the first
Parallel/serial conversion circuits 11A, 11B will be described with reference to FIG. 7 when the serial/parallel conversion circuits 7A, 7B of the noise removal circuit shown in the figure are used as explained in connection with FIG. 6 above.

61, 63, and 65, in the case of the parallel/serial conversion circuit 11A for the luminance signal, the delay amount is the sampling period,
The delay amount is equal to the sampling period and one horizontal period, and in the case of the parallel/serial conversion circuit 11B for the carrier color signal, the delay amount is four times the sampling period, four times the sampling period, and the sum of one horizontal period and twice the sampling period. is a delay circuit equal to .

In the parallel/serial conversion circuits 11A and 11B, the input signal S'I2 from the input terminal 46 is transferred to the delay circuit 6.
1 and delay it, and its delayed output and input terminal 45
The input signal S'i1 from the input terminal 48 is added to the input signal S'i1 from the input terminal 48 in the synthesizer 62, and the input signal S'I4 from the input terminal 48 is supplied to the delay circuit 63, and the delayed output and the input signal S' from the input terminal 47 are added.
13 in a synthesizer 64 and supplied to a delay circuit 65, and the delayed output and the output signal from the synthesizer 62 are added in a synthesizer 66 to obtain an output signal S''1 at an output terminal 55. Next, the orthogonal transform circuit 8A in FIG.
8B and the inverse conversion circuits 10A and 10B will be explained with reference to FIG.

In this case, since the orthogonal transform circuits 8A and 8B use Hadamard transform circuits, the inverse transform circuits 10A and 10B also have the same configuration. Furthermore, as mentioned above, the serial and
Since the parallel conversion circuit 7B is configured so that the parallel signals obtained therefrom have the same level, there is no need to make the order of the orthogonal conversion circuit 8B for the carrier color signal particularly high, and the orthogonal conversion circuit for the luminance signal does not need to be particularly high. The order is the same as for 8A. The same can be said of the inverse conversion circuit 10B. In this example, conversion circuits 8A, 8B, 10A
, 10B, a fourth-order Hadamard transform circuit is used.
The fourth-order Hadamard transformation matrix H4 is as follows. Note that the 2nd to 4th rows of the matrix in equation (8) can be interchanged.

In FIG. 8, 68 to 71 are input terminals, 72 to 79 are combiners, of which 72, 74, 76, and 79 are addition combiners,
73, 75, 77, and 78 are subtractive synthesizers, and 80 to 83 are output terminals.

Then, in the orthogonal transform circuits 8A and 8B, the input terminal 68
When the input signals Sil to Si4 are supplied to the output terminals 80 and 71, the output signals Sll to Sl4 that satisfy the following equation are output to the output terminal 80.
~83. Next, let us examine the properties of the orthogonal transform outputs Sl, ~Sl4 obtained in this way.

Among the orthogonal transform outputs, the low-order transform output, ie, S'11 in this example, tends to contain many low frequency components, whereas the high-order orthogonal transform output, ie, Sl2
~Sl4 tends to include high frequency components. 8th order, 1
This tendency is even stronger in the case of high-order transformation matrices such as 6th order.

In other words, by orthogonally transforming a video signal, this video signal is concentrated in the low-order orthogonal transform output, and the higher the order, the less it appears in the orthogonal transform output. It means something.

On the other hand, noise contained in a video signal obtained from a VTR or the like is distributed over almost the entire band and is considered to be random noise.

Therefore, when a video signal with such noise is orthogonally transformed, the noise components will be distributed with approximately uniform amplitude in each orthogonal transform output, but the orthogonal transform output with a low order will be
/N is good, and the noise component becomes dominant in the high-order orthogonal transform output, so the S/N deteriorates. What can be said from these things is that if the level of the orthogonal transform output is high, it can be regarded as a video signal component. Conversely, if the level of the orthogonal transform output is low, it can be regarded as a noise component. Moreover, as mentioned above, the S/N deteriorates in high frequency components, and since the human visual characteristics for these high frequency components generally deteriorate, it is difficult to reproduce the high frequency region. Even if the reproducibility is poor, it does not have much influence on the reproduced image.From the above, if the orthogonal transform output is at a low level that is approximately determined by the frequency spectrum of the noise, it can be considered as a noise component. It would be better to consider it as such and remove it.

In the case of the inverse conversion circuits 10A and 10B, the input signal S is input to the input terminals 68 to 71.

By supplying signals 1 to SO4, output signals S'i1 to S'I4 satisfying the following equations are obtained at output terminals 80 to 83. Next, the specific structure of the nonlinear circuits 9A and 9B shown in FIG. 1 will be explained with reference to FIGS. 9 to 11. The overall configuration of nonlinear circuits 9A and 9B in FIG.
Output signal S supplied from ~95 to inverse conversion circuits 10A and 10B. I am trying to obtain 1~SO4. In this case, except between the input terminal 85 and the output terminal 92, between the input terminal 86 and the output terminal 93, between the input terminal 87 and the output terminal 94,
When considering an analog signal between the input terminal 88 and the output terminal 95 as a nonlinear circuit as shown in FIG. Coring circuits 89, 90, and 91 are provided in which the relationship between the input level and the output level is linear. Since these coring circuits 89 to 91 are digital circuits in this example, they adopt a configuration as shown in FIG. 11 as an example. T1 (SIGN) is a sign bit input terminal, T1 (MSB) to T1 (LSB) are bit input terminals for the most significant digit to the least significant digit, T2 (SIGN) is a sign bit output terminal, T2 (MSB) to T2 (LSB) )
are bit output terminals for the most significant digit to the least significant digit. Then, the corresponding input/output terminals T1 (SIGN) and T2 (SI
GN), between T1 (MSB), T2 (MSB)...
. . , AND circuits A, , Al, . . . , A1 are inserted between T1 (LSB) and T2 (LSB), respectively. A comparator circuit CMP is provided, and the input terminal Tst
, and the input terminals T1 (SIGN) and T1 (
MSB), ..., T1 (LSB) are compared bit by bit, and the comparison outputs are supplied to the above-mentioned AND circuits A8, Al, ..., An. be done. Then, input terminals T1 (SIGN), T1 (MSB
), . . . , T1 (LSB), when the V level of the input signal constituted by each bit signal is less than a predetermined value, the AND circuit A8 is output by the output of the comparison circuit CMP.
, Al, . . . , AO are all closed, and when the level of the input signal is above a predetermined value, the AND circuit As, Al, . All of An is opened. According to the present invention described above, since a serial/parallel conversion circuit is used in which carrier color signals sampled at substantially the same level are output in parallel, an orthogonal conversion circuit with a simple configuration can be used as the orthogonal conversion circuit. It is possible to obtain a carrier color signal noise removal circuit that can perform the following.

Furthermore, according to the embodiments described above, it is possible to obtain a color video signal noise removal circuit using an orthogonal transform circuit that does not impose restrictions on the conversion order or the sampling frequency when quantizing and processing the video signal. can.

Note that the sampled luminance signal and carrier color signal may be obtained by separating a color video signal (analog signal) into a luminance signal (analog signal) and carrier color signal (analog signal) and then sampling the same. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIGS. 2, 3, 4, 5, 6, 7, 8, and 9 are block diagrams, respectively. 10 is a characteristic curve diagram, and FIG. 11 is a block diagram showing a specific example of a part of FIG. 1. 5 is a separation circuit, 6A and 6B are luminance signal and carrier color signal noise removal circuits, 7A and 7B are first and second series-to-parallel conversion circuits, 8A and 8B are first and second orthogonal conversion circuits, 9
A, 9B are the first and second nonlinear circuits, 10A, 10B
are first and second inverse conversion circuits, and 11A and 11B are first and second parallel/serial conversion circuits.

Claims (1)

[Claims] 1. A serial/parallel converter circuit to which a carrier color signal sampled at a predetermined sampling frequency is supplied and carrier color signals sampled at substantially the same level are output in parallel, and the serial/parallel converter circuit. an orthogonal transformation circuit to which the output of the orthogonal transformation circuit is supplied, a nonlinear circuit to which the output of the orthogonal transformation circuit is supplied and noise is removed, an inverse transformation circuit to which the output of the nonlinear circuit is supplied, and an output of the inverse transformation circuit. 1. A carrier color signal noise removal circuit comprising: a parallel-to-serial conversion circuit to which a carrier color signal is supplied; and a carrier color signal from which noise has been removed is obtained from the parallel-to-serial conversion circuit.